YM2610

The YM2610 is a sound synthesis and playback chip made by Yamaha, found in all versions of the NeoGeo hardware.
It was later merged with other chips in NEO-YSA and NEO-YSA2, which are used on some versions of the NeoGeo CD, the CDZ, the MV1C and on ROM-Only boards.

The YM2610 requires a YM3016 external DAC (Digital to Analog Converter) chip for the FM and ADPCM sounds. The only direct analog output is for the SSG mono sounds. Both analog signals are then mixed together before amplification.

Multiplexed ADPCM bus

Access to the V ROMs are made via partly multiplexed buses. See YM2610 bus timing for more details about the access sequences.

The SDRMPX and SDPMPX signals are used to control latches or the PCM chip in cartridges to demultiplex address and data. When SDROE or SDPOE goes low, SDRAD* and SDPAD* are tristated so that the V ROMs can output data.

SDRA* for ADPCM-A

SDRMPX edge

SDRAD*

SDRA*

0

1

2

3

4

5

6

7

8

9

20

21

22

23

Low to high

0

1

2

3

4

5

6

7

8

9

?

?

?

?

High to low

10

11

12

13

14

15

16

17

18

19

20

21

22

23

SDPA* for ADPCM-B

SDPMPX edge

SDPAD*

SDPA*

0

1

2

3

4

5

6

7

8

9

10

11

Low to high

0

1

2

3

4

5

6

7

8

9

10

11

High to low

12

13

14

15

16

17

18

19

20

21

22

23

24 address bits allow for 16MiB max V ROMs (without bankswitching).

Trivia

A lot of games have several recordings of the same instrument playing different notes, rather than having only one sample and change the ADPCM-B playback frequency to vary its pitch. (Trumpet in Viewpoint, electric guitar in Super Sidekicks). Why ?

Nazca's sound drivers are able to use the SSG channels for music playback. (Maybe all can ?)